OO 


GIFT   OF 


Grain  Dust  Explosion 
Prevention 


, 


UNITED  STATES  GRAIN  CORPORATION 

n 

In  Co-operation  with  the 
Bureau  of  Chemistry 

UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 


DUST  from  grain  will  explode  when 
mixed  with  air  in  proper  propor- 
tions and  ignited  by  sufficient  heat 
or  flame.  The  hazards  of  a  dusty 
and  dirty  plant  are  very  great.  The 
only  safe  guaranty  against  a  dust 
explosion  is  to  practice  "good  house- 
keeping" and  keep  your  plant  clean 
at  all  times.  It  is  your  duty  to 
protect  not  only  your  property  but 
the  health  and  lives  of  your  employes 


NEW   YORK 
June  1920 


vo 

CO 


ORGANIZATION  OF  DUST  EXPLOSION  PREVENTION 

CAMPAIGN 

In  carrying  on  the  dust  explosion  prevention  campaign  for  the  year 
1919-20  the  United  States  was  sub-divided  into  four  districts:  Eastern, 
Northwestern,  Central  and  Pacific  Coast.  The  personnel  of  this  cam- 
paign was  as  follows: 

UNITED  STATES  GRAIN  CORPORATION 
DR.  J.  W.  T.  DUVEL,  New  York,  in  Charge 

MR.  H.  E.  ROETHE,  JR Washington,  D.  C. 

MR.  J.  O.  REED Washington,  D.  C. 

MR.  H.  R.  BROWN Washington,  D.  C. 

MR.  G.  D.  WITHER Washington,  D.  C. 

MR.  E.  L.  RILEY Buffalo,  N.  Y. 

MR.  P.  L.  MANN New  Orleans,  La. 

MR.  VERNON  FITZIMONS Minneapolis,  Minn. 

MR.  PAUL  E.  BRADY Minneapolis,  Minn. 

MR.  W.  B.  LIND Minneapolis,  Minn. 

MR.  G.  A.  HIBBARD Chicago,  111. 

MR.  G.  H.  RICE Chicago,  111. 

MR.  H.  J.  HELMKAMP Kansas  City,  Mo. 

MR.  M.  E.  McCoLLAM San  Francisco,  Cal. 

MR.  G.  P.  BODNAR Portland,  Ore.     , 

U.  S.  DEPARTMENT  OF  AGRICULTURE 

MR.  D.  J.  PRICE, 

Engineer  in  Charge  of  Dust  Explosion  Investigations. 
U.  S.  Bureau  of  Chemistry, 
Washington,  D.  C. 

DR.  H.  H.  BROWN, 

Organic  and  Physical  Chemist, 
U.  S.  Bureau  of  Chemistry, 
Washington,  D.  C. 

416813 


GRAIN  DUST  EXPLOSION   PREVENTION 


CONTENTS 

PAGE. 

INTRODUCTION    5 

EDUCATIONAL   WORK    6 

Pledge  cards  7 

Meetings  in  grain  center 9 

Cooperation  with  Canadian  Government 9 

INSPECTION  OF  PLANTS 9 

Improvement  in  condition  of  plants 13 

LITERATURE  15 

RESULTS  OF  CAMPAIGN 18 

EXPLOSIONS  DURING  CAMPAIGN 19 

Buffalo,  N.  Y 19 

Port  Colborne,  Ont.,  Can'. 20 

Kansas  City,  Mo 21 

Spice  dust  Explosion 22 

Aluminum  dust  Explosion 23 

Boissevain,  Man.,  Can 24 

Buffalo,  N.  Y. 24 

Denver,  Colo 25 

EXPERIMENTAL  WORK   25 

Theory  of  dust  explosions 25 

Density  of  dust  cloud 25 

Source  of  ignition 26 

Velocity  of  propagation  of  explosion 26 

Pressures  developed  in  explosions 26 

Conditions  for  explosions 26 

Propagation  of  the  explosions 26 

Prevention  of  explosions 

Large  scale  tests 

Electrical  equipment  and  dust  explosions 28 


GRAIN  DUST  EXPLOSION  PREVENTION 


INTRODUCTION 


The  Government  first  gave  consideration  to  the  dangers  from  grain 
dust  explosions  and  fires,  as  a  result  of  a  disastrous  explosion  in  a  feed 
grinding  plant  at  Buffalo,  New  York,  in  1913.  As  a  result  of  this  explo- 
sion, a  series  of  investigations  were  conducted  by  the  Bureau  of  Mines 
of  the  United  States  Department  of  the  Interior,  in  cooperation  with 
the  milling  and  grain  interests,  with  the  view  of  determining  the  causes 
of  such  explosions  and  fires,  and  to  devise  methods  for  their  prevention. 
Subsequently  this  project  was  turned  over  to  the  Bureau  of  Chemistry 
of  the  United  States  Department  of  Agriculture,  and  much  valuable 
information  brought  together  relative  to  explosions  and  fires  in  grain 
elevators,  flour  mills,  threshing  machines (a)  in  the  Pacific  Northwest 
and  in  cotton  gins(b)  of  the  South. 

The  importance  of  continuing  and  extending  these  investigations  was 
fully  realized  at  the  beginning  of  the  war,  in  order  that  the  country's  food 
supply  might  be  fully  protected  against  the  hazards  of  dust  explosions 
and  fires.  Accordingly  the  United  States  Department  of  Agriculture  and 
the  United  States  Food  Administration  inaugurated  an  extensive  educa- 
tional campaign,  in  the  Fall  of  1917,  to  provide  the  owners  and  operators 
of  mills,  elevators  and  threshing  machines,  with  the  information  avail- 
able, so  that  the  losses  resulting  from  dust  explosions  might  be  reduced 
to  a  minimum.  The  necessity  for  this  undertaking  was  strongly  empha- 
sized by  several  disastrous  dust  explosions  which  occurred  between 
March,  1916,  and  October,  1917,  resulting  in  the  destruction  of  four  of 
the  largest  grain  and  cereal  plants  in  the  United  States  and  Canada,  to- 
gether with  the  loss  of  twenty-four  lives.  The  dust  explosion,  together 
with  the  fire  which  followed,  in  one  of  these  plants  (Brooklyn,  New 
York),  was  of  special  significance  at  the  time  in  that  it  resulted  in  the 
destruction  of  a  quantity  of  grain  equivalent  to  bread  rations  for  an  army 
of  200,000  men  for  an  entire  year,  and  at  the  same  time  most  seriously 
crippled  facilities  badly  needed  for  loading  grain  for  overseas  shipment. 


(a)  Department  of  Agriculture   Bulletins  379  and  681,  and   Circular  98. 

(b)  Department  of  Agriculture  Circular  No.  28. 


The  workmen  in  this  plant  were  not  generally  familiar  with  the  causes  of 
dust  explosions  and  fires  and  methods  that  could  be  adopted  for  their 
prevention. 

The  United  States  Grain  Corporation  assumed  financial  control  of 
the  grain  dust  explosion  campaign  in  July,  1919,  to  make  sure  that  the 
Government's  stocks  of  wheat  were  fully  protected  at  all  times;  other- 
wise the  work  would  have  lapsed  June  30,  1919,  with  the  termination  of 
the  war  emergency  provision  granted  by  Congress  to  carry  on  this  work 
as  a  part  of  the  food  conservation  program.  Since  this  time,  the  United 
States  Grain  Corporation,  in  cooperation  with  the  Bureau  of  Chemistry 
of  the  United  States  Department  of  Agriculture,  has  carried  on  an  exten- 
sive campaign  to  assist  in  removing  dangerous  conditions  in  plants  carrying 
Government  grain  and  flour  stocks,  and  also  to  familiarize  the  grain  and 
milling  interests  with  the  true  nature  and  means  of  prevention  of  dust 
explosions  and  fires.  The  aim  has  been  to  lessen  the  inherent  hazards 
in  the  grain  industry.  Throughout  this  campaign  active  cooperation  has 
been  given  by  many  agencies  and  commissions  engaged  in  explosion  and 
fire  prevention  activities,  and  this  opportunity  is  taken  to  acknowledge 
our  indebtedness  to  these  organizations,  as  well  as  to  the  grain  and  mill- 
ing interests,  for  the  excellent  assistance  rendered. 


EDUCATIONAL    WORK 

In  addition  to  the  regular  inspection  of  plants  carrying  Government 
stocks,  an  effort  was  made  to  impart  to  the  employes  of  elevators  and 
mills  special  information  on  the  subject  of  dust  explosions  and  fires.  In 
the  war  emergency  campaign  all  mills  with  capacity  of  approximately  50 
barrels  or  more,  and  elevators  over  25,000  bushels  capacity,  were  visited. 
In  the  campaign  carried  on  by  the  Grain  Corporation  attention  has  been 
directed  primarily  to  plants  where  Government  stocks  were  stored.  The 
work  has  been  extended,  however,  to  outside  plants  as  time  permitted. 

The  employes  in  the  plants  were  acquainted  with  the  causes  by  which 
explosions  can  be  produced,  with  special  reference  to  the  simple  causes 
within  the  control  of  the  workmen,  such  as  a  lighted  match,  smoking,  use 
of  open  flames,  careless  use  of  electric  lights,  etc.  This  was  done  in 
many  cases  by  a  direct  "  heart  to  heart  "  talk  with  the  men  either  indi- 
vidually or  in  group  meetings,  on  the  working  floors  or  in  convenient 
parts  of  the  plants.  In  order  to  familiarize  the  men  with  the  extent  of 
damage  done  by  previous  explosions,  a  series  of  specially  prepared  photo- 
graphs showing  views  of  damaged  plants  in  which  there  had  been  ex- 
tensive losses  of  life,  grain  and  property  were  used. 

Whenever  it  was  possible  to  assemble  a  number  of  the  employes, 
either  at  the  noon  hour,  or  by  special  arrangement  with  the  management, 
illustrated  lantern  slide  lectures,  showing  results  of  experimental  work, 
and  also  effects  of  recent  explosions,  similar  to  photographs  referred  to 


above,  were  given.  In  addition  to  the  lecture,  various  demonstrations 
of  dust  explosions  were  produced  to  show  the  men  how  readily  a  violent 
explosion  may  result  from  an  apparently  simple  cause.  Two  demonstra- 
tions in  particular  impressed  the  men  effectively  and  aroused  their 
interest.  In  one  case  a  dust  explosion  was  produced  in  a  specially  pro- 
vided miniature  grain  elevator  by  blowing  dust  onto  an  open  flame,  as 
shown  in  Figure  1.  In  the  other,  various  common  dusts  were  readily 


U.S. GRAIN  COR*»ORATIO« 

ELECTOR. 


FIG.    1. — Dust  Explosion   Demonstration — produced  by  blowing  dust  into  an   open   flame  in  a 

miniature  elevator. 

ignited  by  sifting  through  a  piece  of  cheesecloth  onto  a  burning  match. 
In  order  to  remove  any  doubt  regarding  the  nature  of  the  dust  used  in 
the  demonstrations,  the  workmen  were  asked  to  collect  dust  from  various 
parts  of  the  plant.  In  many  instances  samples  of  the  dust  which  the 
employe  had  to  work  with  and  handle  daily  were  presented  for  testing. 
The  effect  of  the  explosion  on  the  workmen  in  these  cases  was  very 
marked.  From  expressions  made  by  the  men  it  could  be  seen  that  they 
would  not  forget  the  lesson  and  would  do  all  they  could  to  prevent 
dangerous  conditions. 


Pledge  Cards 

At  the  close  of  the  lecture  and  demonstrations,  or  during  the  inspec- 
tion trip  through  the  plant,  the  moral  support  of  the  workmen  was 
enlisted  by  having  them  sign  pledge  cards  as  shown  in  Figure  2. 


ct. 


UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 

AND 

UNITED  STATES  FOOD  ADMINISTRATION 

(IF  YOU  HAVE  ALREADY  SIGNED.  PASS  THIS  CARD  ON  TO  A  FELLOW  EMPLOYEE) 

To  prevent  grain  dust  explosions  and  fires  in  the  mills  and  elevators  in  which 
I  am  employed,  1  agree  personally  to  observe  preventive  measures  and  to  use 
every  effort  and  influence  to  induce  others  to  take  all  possible  precautions.  1 
make  this  promise  in  the  realization  that  carelessness  may  result  in  loss  of  life,  loss 
of  food  needed  by  the  Nation,  and  destruction  of  factories  needed  to  produce  food. 


Name 

Firmer  Company. 

City- 


State - 


tOPROTEC^YO^MlLLANl) 

Failure  to  observe  these  reasonable  rule* 
may  result  in  dust  explosions  or  fires  which 
may  cause  loss  of  life  and  Will  cause  loss  of 
food  needed  by  the  Nation  t  > 

1.  Smoking  and  lighted  matches  have 
caused  many  of  our  greatest  fires  and  ex-* 
plosions. 

Do  not  smoke  while  in  or  near  the  mill 
or  elevat"*-- 


2.  An  open  flame  will  cause  a  dust  ex- 
plosion and  fire  in  a  dusty  mill  or  elevator. 

Do  not  carry  any  open  flame,  lantern,  or 

torch  into  a  dusty  atmosphere. 
Do  not  lower  lanterns  or  open  flames  into 

Do  not  lower  unprotected  electric  light 
bulbs  into  dusty  bins;  the  bulb  may 
break,  making  a  spark  that  will  ignite 
the  dust. 

3.  Dust  and  dirt  invite  dust  explosions. 
The  records  show  that  there  are  six  times 
as  many  fires  in  dirty  mills  and  elevators  as 
in  clean  ones. 

See  that  no  dust  accumulates  en  beams, 
machines,  pulleys,  or  floors  in  the  de- 
partment where  you  are  working. 

4.  Elevator      choke-ups      are      frequent 
causes  of  fires  and  explosions.     In  many 
cases   choke-ups   have   led   to  fires  which 
destroyed  over  a  million  dollars'  worth  of 
grain  and  property. 

Examine  all  elevators  and   conveyors  in 


page,  or  other 

A  LITTLE  CARE  MAY  AVERT  A 
DISASTROUS  EXPLOSION. 


FIG.  2. — Pledge    card   signed   by    workmen. 

(a)  Front   of   card. 

(b)  Back   of   card. 


A  ready  response  was  always  secured  and  large  numbers  of  these 
cards  were  signed  by  the  employes.  By  so  doing  they  promised  to  observe 
the  precautions  designed  for  the  prevention  of  these  explosions.  The 
cards  were  forwarded  to  the  Washington  office,  and  their  receipt  imme- 
diately acknowledged,  with  the  name  and  address  of  the  workmen  in- 
serted on  the  card,  as  shown  in  Figure  3.  It  is  believed  that  the  work- 
men adhered  to  their  promises  and  were  responsible  in  many  instances 
for  the  removal  of  dangerous  conditions  which  might  have  resulted  in 
explosion  and  fire. 


UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 

AND 

UNITED  STATES  FOOD  ADMINISTRATION 
WASHINGTON,  D.  C. 

Mr.   ffoe  Taylor, 

340  TSforth  Duncan  St., 

Chicago,   111. 
Dear  Sir: 

This  is  to  acknowledge  receipt  of  the  card,  recently  signed  by  you,  in  which 
you  personally  agree  to  observe  preventive  measures  and  to  use  every  effort  and 
influence  to  induce  others  to  take  all  precautions  to  prevent  grain-dust  explosions 
and  fires  in  mills  and  elevators  in  which  you  are  employed.  By  signing  this  card 
and  carefully  observing  the  pledge  made  thereon,  employees  of  mills  and  elevators 
are  actively  cooperating  with  the  United  States  Department  of  Agriculture  and 


the  United  States  Fo 
WIN  THE  WAR. 


Administration  in  their  effort  to  SAVE    FOOD    AND 


HERBERT  HOOVER 
Food  Administrator 


D.  F.  HOUSTON 
Secretary  of  Agriculture 


FIG.  3. — Card  acknowledging  pledge  of  workmen. 

8 


Meetings    in    Grain    Centers 

In  addition  to  presenting  the  dust  explosion  prevention  work  to 
the  employes  in  the  plants,  it  was  considered  desirable  to  acquaint  the 
owners  and  operators  with  the  hazards.  As  it  was  impossible  to  stage 
large-scale  demonstrations  all  over  the  country,  specially  arranged  motion 
pictures  showing  the  results  of  large  scale  dust  explosion  tests,  as  de- 
scribed on  page  27,  were  shown  to  the  grain  men  in  various  sections 
of  the  United  States.  While  the  small  scale  demonstrations  of  dust 
explosions  served  their  purpose  well,  they  did  not  show  fully  the  rate  at 
which  an  explosion  might  propagate  through  the  plant.  The  motion 
picture  reels  also  contained  views  of  plants  damaged  by  explosions  and 
fire  together  with  measures  of  prevention.  The  work  was  also  pre- 
sented at  conventions  of  fire  protection,  conservation,  and  similar  asso- 
ciations. These  conventions  in  many  instances  included  not  only  grain 
men  but  firemen  and  insurance  representatives  as  well.  Numerous  re- 
quests for  presentation  of  the  work  were  received  from  associations  of 
firemen,  in  order  to  obtain  information  to  assist  in  the  prevention  of  dust 
explosions  during  the  progress  of  fire  fighting. 


Cooperation    with    Canadian    Government 

In  connection  with  the  series  of  meetings  held  in  the  larger  grain 
centers  of  the  United  States,  as  a  result  of  a  request  from  the  Dominion 
Fire  Commissioner,  a  special  dust  explosion  prevention  meeting  was 
held  at  Fort  William,  Ontario,  in  November,  1919.  This  meeting  was 
attended  by  a  large  number  of  Government,  provincial  and  city  officials, 
as  well  as  representatives  of  the  Canadian  grain  and  milling  industries 
and  insurance  companies. 

Interest  in  dust  explosion  prevention  was  aroused  in  Canada  by 
an  explosion  in  August,  1919,  in  a  large  grain  elevator  at  Port  Colborne, 
Ontario,  operated  by  the  Dominion  Government.  The  explosion  was  in- 
vestigated in  cooperation  with  the  Canadian  Government  officials  and 
assistance  rendered  in  the  development  of  precautionary  measures  in 
the  rebuilding  of  the  plant. 


INSPECTION    OF    PLANTS 

As  previously  stated,  this  campaign  was  undertaken  primarily  for 
the  protection  of  the  Government  grain  and  flour  stocks  against  the 
hazards  of  dust  explosions  and  fires.  For  this  purpose,  regular  inspec- 
tions were  made  of  the  mills  and  elevators  where  Grain  Corporation  stocks 
were  stored.  Other  plants  were  likewise  visited  frequently  in  order  that 
the  country's  food  supply  might  be  fully  protected.  If  conditions  seemed 
hazardous  in  any  respect,  definite  suggestions  for  remedying  them  were 


made  to  the  official  in  charge  of  the  plant.  At  the  time  of  the  first  visit 
to  each  establishment,  the  inspector  filled  out  a  complete  report  on  the 
following  form  provided  for  the  purpose : 


GRAIN  DUST  EXPLOSION  CAMPAIGN 

U.  S.  DEPARTMENT  OF  AGRICULTURE 

BUREAU  OF  CHEMISTRY  AND  BUREAU  OF  MARKETS 


District Date Inspected  by 

Name   of    Company 

Office    Address :      Street City State .... 

Plant  Address:     Street City State. . 

Kind  of  Plant Mgr 

Supt Capacity No.     Employees 

Construction :    Wood Brick  or  Stone Concrete Steel 

Remarks 

Bins :      Open Covered Remarks 

Elevators :    Wood Steel Combination 

Discharge  to  Bin:    By  Spout Belt Steel  Conveyor.  .  .  . 

Remarks 

Is  Grain  Cleaned  before  Storage  ?     Yes No 

Remarks 

Dust   Collectors :     Location Cloth 

Cyclone Dust    Room 

Remarks 

Suction  System:    On  Bins Elevator  Heads Conveyors.... 

Remarks   

Grinding  Mills :    Type 

Discharge  to:    Elevator Conveyor Bin 

Misc 

Any    Explosion    Protection 

Remarks   

Power  Plant :    Steam Electric Gasoline Misc. .  . 

Lighting :    Type Method   of    Installation 

Remarks 

General   Condition   of  Plant 

Remarks   

Are    Sweepers    Employed  ? 

General  Remarks   


No.  of  Cards  Signed No.  of  Circulars  Desired 

No.    of    Posters    Desired , 

Suggested  Recommendations  for   Explosion   and  Fire   Prevention 


Copies  of  this  report  were  then  sent  to  the  district  office  and  also  to 
Washington,  where  they  were  recorded.  On  all  subsequent  visits  the  in- 
spector used  a  shorter  form  on  which  he  noted  only  the  rating  for  equip- 

10 


ment  and  maintenance  and,  when  necessary,  his  recommendations  to  the 
company,  as  well  as  any  changes  in  equipment  since  the  preceding  inspec- 
tion. 


GRAIN     DUST    EXPLOSION 
U.    S.     GRAIN 
U.    S.    DEPARTMEN1 

District  Date 

AND    FIRE    PREVENTION 
CORPORATION 
'    OF    AGRICULTURE 

Name   of   Company  

Address  :     City  

State  

Manager  

Supt      

Kind  of  Plant 

Equipment  Maintenance 

Recommendations  Made  to.  

Recent    Changes,    Recommendations,    etc  

In  making  these  reports  the  following  series  of  letters  was  used  to 
classify  the  equipment  and  maintenance  of  the  plant: 

Equipment  Maintenance 

A.  Modern,  first-class,  up-to-date  appliances  A.  Good 

B.  Fair,  not  new.  B.  Fair 

C.  Old  and  not  representative  C.  Poor 

A  well-constructed  plant,  with  modern  mechanical  appliances,  would 
be  given  "A"  for  equipment.  If  precautionary  measures  were  being 
carried  out,  and  the  explosion  hazard  recognized,  the  plant  received  "A" 
for  maintenance.  The  classification  for  such  a  plant  would  then  be 
"AA."  If  the  maintenance  was  not  up  to  the  standard  and  the  dust  con- 
ditions looked  after  in  only  a  "  fair  "  manner,  the  classification  would  be 
"  AB."  If  the  plant  was  well  equipped,  but  found  in  a  dirty,  dusty,  or 
poor  condition,  it  would  receive  a  grade  of  "  AC."  In  many  cases,  how- 
ever, equipment  which  was  not  strictly  modern  but  was  rendering  satis- 
factory service  was  put  in  the  "  B  "  class,  to  distinguish  it  from  that  of 
newer  type  or  design.  If  the  plant  was  well  maintained  it  would  be 
classed  as  "  BA,"  while  "  BB  "  and  "  BC  "  represented  the  intermediate 
and  poor  classes,  respectively.  Old  type  plants,  in  which  the  equipment 
had  been  installed  for  some  time  fell  in  the  "  C  "  class.  When  it  was 
well  maintained  and  particular  attention  was  paid  to  the  removal  of  the 
dust  conditions,  the  plant  would  be  placed  in  the  "  CA  "  class.  Similarly, 
"  CB  "  and  "  CC  "  represented  the  other  grades  of  upkeep  and  mainte- 
nance. 

11 


United  States 
Department  ofAgricultur 


SAVE  LIVES 


United  States 
Food  Administration 


SAVE  FOOD-SAVE  PROPERTY 


Six  Recent  Dust  Explosions  and  Fires  in  Mills  and  Elevators 

Killed  39  Persons  and  Injured  60.    They  Destroyed  2,500,000 

Bushels  of  Grain,  and  Property  Worth  $8,000,000 


Keep  Your 

Mill  and 

Elevator 

Free  from 

Dust  and  Dirt 


Dust-free 
Mills  and 
Elevators 
are  Explo- 
sion-proof 


Elevator  explosions  and  fires  sometimes  destroy  enough  grain  to  feed  a  large  army  for  a  year 


This  large  cereal  plant  was  completely  destroy 


following  a  dust  e 


PROTECT  YOUR  MILL  AND  ELEVATOR 

4  little  care  may  avert  a  disastrous  explosion.    Observe  the  following  rules: 


1.  Do  not  smoke  or  carry  matches   in    or   near  the   buildings. 
Smoking  and   lighted   matches    cause    explosions    and    fires* 

2.  Do  not  use  open  flames,  torches,  candles,  lanterns  and  un- 
protected electric  light  bulbs  in  a  dusty  atmosphere  or  when 
examining  bins  and  elevator  legs. 


4.  Do  not  let  dust  accumulate  on  beams,  machines,  pulleys 
or  floors.  Dust-free  Mills  and  Elevators  are  explosion  -  proof. 

4.  Examine  elevators  and  conveyors  often.  Elevator  choke-upt 
often  cause  explosions  and  fires.  Report  immediately  any  »light 
rubbing,  slipping,  or  other  trouble. 


For  further  information  regarding  grain  dust  txflosions  virile  to  tat 

U.  S.  Department  of  Agriculture,  Bureau  of  Chemistry,  Washington,  D.  C. 

This  Company  and  it*  Employee!  are  Co-operating  in  the  Control  of  Du.t  Explosions  and  Firei 


FIG.  4. — Reproduction  of  first  poster  used  in  Grain  Dust  Explosion  Prevention   Campaign. 

(Original  16  x  24  inches.) 


12 


These  reports  also  were  sent  immediately  to  district  headquarters  and 
then  to  Washington,  so  that  the  officials  in  charge  could  at  all  times  keep  in 
close  contact  with  the  general  conditions  of  the  mills  and  elevators 
throughout  the  country.  By  comparison  with  previous  reports,  it  was 
possible  to  determine  whether  or  not  the  condition  of  the  elevator  was 
improving  and  whether  the  precautionary  measures  previously  recom- 
mended had  been  adopted. 

Improvement    in    Condition    of    Plants 

That  conditions  in  the  elevators  and  mills  inspected  were  materially 
improved  as  a  result  of  the  recommendations  made  to  the  officials  in 
charge  is  evident  from  the  reports  turned  in  by  the  field  men.  The  fol- 
lowing table  gives  a  few  typical  cases  of  the  results  of  this  phase  of  the 
work. 

Elevator  Visit  Date  Grade 

1  1  September  4,  1919 AC 

(Middle  West)  2  September  26,  1919 AB 

3  February  18,  1920 A  A 

2  1  September  23,  1919 AC 

(East)  2  November  29,   1919 AB 

3  March  5,  1920 A  A 

3  1  November  26,   1919 B  C 

(East)  2  March  1,  1920 B  B 

3  March  20,  1920 B  A 

4  1  September  11,  1919 CC 

(West)  2  October  17,  1919 CB 

3  February  4,  1920 C  A 

5  1  August  19,  1919 A  A 

(East)  2  December  17,  1919 AA 

3  January  28,    1920 A  A 

4  April  13,  1920 A  A 

Elevators  1  and  2,  although  well  constructed  and  equipped  with 
modern  machinery,  were  poorly  maintained  at  the  time  of  the  first  inspec- 
tion. As  a  result  of  following  the  recommendations  made  by  the  inspec- 
tor, conditions  were  so  improved  that  when  the  last  inspection  was  made 
the  plants  received  the  grade  of  "  AA." 

Although  elevator  3  remained  in  class  "  B  "  (medium)  for  equip- 
ment, it  improved  sufficiently  in  condition  to  rise  from  "  C  "  to  "A"  in 
maintenance. 

Elevator  4  was  poorly  equipped  and  very  poorly  maintained  at  time 
of  first  inspection,  showing  evidence  of  but  little  precaution  against  fires 
and  explosions.  The  information  received  by  the  officials,  however,  en- 
abled them  to  bring  their  grade  up  to  "  B,"  and  finally,  after  they  had 
adopted  additional  methods  of  dust  explosion  and  fire  prevention,  to  "  A," 
the  equipment  in  this  plant  was  not  improved,  remaining  in  the  "  C  " 
grade. 

Elevator  5,  modern  in  construction  and  equipment,  was  found  at  the 
time  of  each  visit  to  be  in  an  excellent  condition  and  provided  with  every 
device  for  minimizing  the  dangers  from  dust  explosions. 

As  this  summary  is  representative  of  the  large  number  of  reports 
received  from  all  over  the  country,  it  may  be  concluded  that  the  recom- 

13 


DUST-FfeEE 


and  Elevators 

EXPLOSION- 
PROOF 


Carelessness 


a  lighted  match 
dusty  machinery 
an  uncovered  candle 

or  lantern 
friction  in  machinery 


Cleanliness 


means  nothing  to 
explode 

protects  workmens'  lives 
saves  property 
saves  food 


lLS,Grain  Cbtporation- 

U.S.  Department  of  Agriculture 

Far  further  information  about  grain  dust  explosion*  write  to  the 
Bureau  of  Chemistry,  -  U.  S.  Department  of  Agriculture 


FIG.    5. -Reproduction  of  second  poster  used  in  Grain  Dust  Explosion   Prevention   Campaign. 
(Original  in   colors,    !4l/2  x  22   inches.) 


14 


mendations  made  in  this  campaign  brought  about  an  improvement  in 
conditions  and  a  decrease  in  dangers  from  explosion  and  fire  in  the 
elevators  and  mills  of  the  United  States. 


LITERATURE 

To  keep  the  dangers  from  explosions  and  fires  before  the  men  at  all 
times,  two  sriking  posters  (Figs.  4  and  5)  were  prepared.  These  posters 
were  mailed  to  every  licensed  elevator  and  mill  and  also  distributed 
through  the  conservation  and  fire  prevention  agencies.  They  were  dis- 
played in  prominent  parts  of  the  plants  and  in  the  frequent  visits  to  the 
elevators  and  mills  it  was  found  that  the  workmen  were  following  the 
precautions  outlined. 

Several  pamphlets  were  also  provided  for  the  workmen  to  read  dur- 
ing their  lunch  hours  or  at  any  spare  moments.  In  the  circular  entitled 
"  Prevent  Grain  Dust  Explosions  and  Fires"  (Fig.  6)  attention  was  di- 
rected to  the  great  loss  of  life,  property  and  foodstuffs  due  to  dust  explo- 
sions, and  a  brief  description  is  given  in  simple  language  of  how  a  dust 
explosion  actually  occurs.  The  employes  were  asked  to  help  reduce  this 
loss  by  observing  the  following  rules : 


PREVENT  GRAIN  DUST 
EXPLOSIONS  AND  FIRES 

IT  IS  POSSIBLE—NECESSARY 


This   Circular  Tells  How  and  Why 


U.  S.  DEPARTMENT  OF  AGRICULTURE 

WASHINGTON.   D.   C. 
1918 


FIG.   6. 


1.  Get  the  dust. 

2.  Prohibit  smoking  and  carry- 

ing matches  in  or  around 
the  mill  or  elevator. 

3.  Use  no  open  flames,  as  gas- 

lights, torches,  lanterns  or 
candles  for  any  purpose 
whatever  in  or  around  the 
mill  or  elevator. 

4.  See  that  all  wires  for  electric 

lighting  are  placed  in  con- 
duits, and  use  only  well- 
protected  globes. 

5.  Do  not  lower  artificial  lights 

into  bins  to  determine  the 
amount  of  grain,  flour  or 
feed  they  contain. 

6.  Keep     all     foreign     material 

from  entering  the  grinding 
machinery. 

7.  Eliminate  static  electricity. 

8.  Look  out  for  elevator  choke- 

ups. 

9.  Do  not  let  elevator  or  con- 

veyor belts  rub. 

10.  Sack  the  ground  material  im- 
mediately or  convey  it  to 
bins  of  small  capacity. 


15 


"  Just  a  Word  About  Grain  Dust  Explosions  "  (Fig.  7)  contains  a 
summary  of  the  dust  explosion  campaign  preceding  September,  1919, 
pointing  out  that  for  a  period  of  19  months  there  were  no  explosions  in 
plants  where  the  workmen  had  pledged  their  support  to  the  work,  while 
disastrous  explosions  had  occurred  in  other  industries.  It  includes  eight 
short  stories  describing  eight  explosions,  illustrated  with  attractive  draw- 
ings, and  gives  the  cause  and  method  of  prevention  in  each  case.  It  fur- 
ther urges  employes  to  adopt 
the  following  dozen  rules 
for  safety: 


ust  a  Word 


1.  Keep  the  plant  clean. 

2.  Inspect   the   plant    frequently 

for  hot  bearings. 

3.  Keep  constantly  on  the  watch 

for  elevator  choke-ups. 

4.  Report       immediately        any 

slight  rubbing,  slipping  or 
other  trouble  with  belts  or 
machines. 

5.  Keep     all     foreign     material 

from  entering  the  grinding 
machinery  by  installing  a 
magnetic  separator. 

6.  Do    not    smoke    while    in    or 

near  the  elevator. 

7.  Do  not  carry  matches   in   or 

near  the  buildings. 

8.  Do  not  allow  an  open  flame, 

lantern  or  torch  in  the  mill 
or  elevator. 

9.  Dp  not  lower  artificial  lights 

into  bins  to  determine  the 
amount  of  grain,  flour  or 
feed  they  contain. 

10.  Prevent  the  accumulation  of 

static  electricity  on  ma- 
chines and  belts  by  proper 
grounding  methods. 

11.  See  that  all  electrical  equip- 

ment is  properly  installed, 
light  bulbs  well  protected, 
switch  and  fuse  boxes  kept 
closed. 

12.  Sack  the  ground  material  im- 

mediately or  convey  it  to 
bins  of  small  capacity. 

Two  small  folders  were  designed  to  call  attention,  in  a  few  words 
and  by  means  of  pictures,  to  the  dangers  of  dust  explosions  and  to  some 
of  the  simple  preventive  measures.  The  folder  entitled  "  Four  Reasons 
Why  You  Should  Be  Careful  "  (Fig.  8),  urges  the  employee  to  follow  a 
few  important  rules  for  the  protection  of  life,  property,  food  and  his 
job.  The  other,  commonly  called  the  "  Capitol  Folder,"  emphasizes  the 
cost  of  carelessness,  and  endeavors  to  impress  upon  the  employee  by  a 
specially  prepared  story,  the  fact  that  one  careful  man  in  a  plant  is  better 
than  a  whole  fire  department.  It  contains  four  rules  for  the  protection 
of  lives,  food  and  property  from  the  dangers  of  dust  explosions. 

16 


Dust 
Explo 

sions 

• am 

f'-TjTlMj 

'sL'ipi 

<$ 


FIG.  7. — Upper  portion  of  this  plant  destroyed  by 
dust  explosion.  From  cover-page  of  pamphlet 
used  in  educational  campaign. 


REASONS 
WHY  YOU 
SHOULD  BE 
CAREFUL 


REASON  No.  1 


Loss  of 
Property. 


REASON  No.  2 


REASON  No.  3 


REASON  No.  4 


Loss  of 
Food. 


HOW  TO 
BE  CAREFUL 

Look  over  the  elevators  and 
conveyors  often,  report  at  once 
any  rubbing,  slipping,  friction,  or 
other  trouble,  no  matter  how 
slight. 

Also  observe  carefully  these 
four  important  DON'TS: 

Never  smoke   in  or  near 

the  mill  or  elevator. 
Never  strika.  a  match  any- 

wliere  on  the  premises. 
Never    use    open    flames, 
torches,     candles,     lan- 
terns,    or     unprotected 
light  bulbs  in  dusty  air 
or  when  examining  bins 
or  elevator  legs. 
Never  let  dust  accumulate 
on  beams,   machines, 
pulleys,  or  floors. 

UNITED  STATES  GRAIN  CORPORATION 

Cooperating  with  the 

United  Stales  Department  of  Agriculture 

Bureau  of  ChemUtrj 


FIG.  8. — Reproduction  of  small  folder  used  in  educational  campaign  to  prevent  destruction 
of  Government  food  supplies  by  dust  explosions  and  fires. 


17 


RESULTS     OF     CAMPAIGN 

The  dust  explosion  and  fire  prevention  work  was  well  received  in 
every  section  of  the  country.  With  the  splendid  cooperation  of  the 
American  mills  and  elevators,  as  well  as  the  various  fire  prevention 
agencies  and  commissions  established  to  conserve  our  food  supply,  the 
campaign  was  most  successful.  During  the  entire  period  of  its  existence 
(about  three  years)  the  United  States  Grain  Corporation  suffered  no 
extensive  explosion  or  fire  losses.  The  fact  that  practically  at  all  times 
the  value  of  the  stocks  in  storage  was  $100,000,000  and  at  certain  times 
approximately  $500,000,000,  shows  the  importance  of  the  saving  thus 
effected. 

During  the  period  of  the  campaign  there  has  been  only  one  disastrous 
explosion  in  a  grain  elevator  where  United  States  Grain  Corporation 
stocks  were  stored.  The  actual  loss  to  Government  grain  in  this  case, 


FIG.  9. — Extensive  damage  resulting  from  explosion  of  starch  dust. 

however,  was  limited  to  about  $25,000.  Since  this  explosion  in  Septem- 
ber, 1919,  there  has  not  been  an  explosion  in  the  last  nine  months  in  a 
plant  where  Government  grain  was  stored  or  handled,  and  where  atten- 
tion had  been  given  to  the  removal  of  explosion  and  fire  hazards. 

While  the  explosion  and  fire  losses  in  the  grain  industry  appear  to 
have  decreased  during  this  special  campaign  period,  reports  indicate  that 
in  other  industries  the  fire  losses  were  considerably  increased.  In  May, 
1919,  a  very  disastrous  explosion  in  a  starch  factory  in  the  Middle  West 
resulted  in  the  loss  of  43  lives  and  property  damage  estimated  at  $3,- 
000,000.  The  wreckage  of  this  explosion  is  shown  in  Figure  9.  In 
August,  1919,  a  large  grain  elevator  operated  by  the  Canadian  Govern- 

18 


ment  was  badly  damaged  by  a  dust  explosion  in  which  10  lives  were  lost 
and  10  injured.  An  explosion  of  aluminum  dust  in  a  factory  in  Wis- 
consin caused  the  death  of  six  girls  and  injuries  to  as  many  others.  Ex- 
plosions of  minor  proportions  have  occurred  during  the  period  in  feed 
mills,  flour  mills  and  other  industrial  plants. 

The  effect  of  enlisting  the  aid  of  the  workmen  is  shown  by  the  fact 
that  during  a  period  of  19  months  (October,  1917,  to  May,  1919)  no 
dust  explosions  occurred  in  any  of  the  plants  where  the  employees  had 
pledged  their  support  to  the  campaign.  In  marked  contrast  to  this  are 
the  five  disastrous  explosions  in  the  United  States  and  Canada  of  the 
preceding  20  months  (March,  1916,  to  October,  1917). 


EXPLOSIONS     DURING     CAMPAIGN 
Buffalo,  N.  Y. 


On  September  12,  1919, 
a  dust  explosion  in  a  feed 
mill  and  elevator  at  Buffalo. 
New  York,  injured  3  men, 
1  seriously,  and  damaged 
property  to  the  extent  of 
$20,000  (Fig.  10). 

The  investigation  showed 
that  the  force  of  the  explo- 
sion traveled  upward,  blow- 
ing out  a  part  of  the  west 
wall  of  the  fourth  floor  as 
well  as  part  of  the  roof  of 
the  lofter  room  at  the  top  of 
the  building,  and  that  a  mus- 
lin cover  used  to  keep  one 
of  the  motors  on  an  upper 
floor  free  from  dust  had 
been  burned.  At  first  it 
was  thought  that  the  explo- 
sion was  caused  by  the  igni- 
tion of  this  muslin  cover  by 
sparks  from  the  motor.  A 
detailed  observation  of  the 
motor,  however,  showed 

that  no  sparks  issued  from  its  brushes  while  it  was  in  operation,  and  that 
it  worked  satisfactorily,  thus  making  it  apparent  that  the  motor  cover 
was  set  on  fire  by  the  explosion.  From  the  nature  of  the  damage  it 
seemed  that  the  explosion  originated  from  an  unknown  cause  at  some 
point  on  the  first  floor  near  an  elevator  leg,  and  propagated  up  to  the 
fourth  floor  where  a  second  and  more  disastrous  explosion  occurred. 


FIG.    10. — Damage  to  upper  floors  resulting  from  dust 
explosion    in   a  feed  mill. 


Port    Colborne,    Ontario,    Canada 


FIG.  11. — Upper  portion  of  grain  elevator  badly  damaged  by  dust 
explosion.  Note  "  trough-like  "  construction  of  interior 
walls  of  bins. 


On  August  9,  1919,  an  explosion  occurred  in  an  elevator  owned  and 
operated  by  the  Canadian  government  at  Port  Colborne,  Ontario,  Canada, 
as  a  result  of  which  10  men  lost  their  lives  and  the  same  number  were 
more  or  less  seriously  injured,  while  the  loss  of  property  was  estimated 
at  $750,000  (Fig.  11). 
The  damage 
wrought  by  the  explo- 
sion was  confined  to 
the  area  above  the 
storage  tanks,  very 
little  damage  being 
done  to  the  basement 
and  storage  section  of 
the  plant.  The  bin 
floor  and  the  roof 
over  the  storage  sec- 
tion were  entirely 
blown  off.  Part  of 
the  side  walls  of  the 
working  tower  was 
demolished,  as  well  as 
a  large  portion  of  the 
roof  of  the  working 

house.  Both  ends  of  the  tower  were  badly  damaged.  In  fact,  the  force 
of  the  explosion  at  these  points  was  so  great  that  heavy  8-inch  steel  "  I  " 
beams  were  carried  some  distance  from  the  plant.  In  some  cases  large 
pieces  of  reinforced  concrete  were  hurled  for  a  distance  of  150  feet.  A 
barge  which  was  being  loaded  with  grain  in  the  slip  on  the  east  side  of 
the  plant  was  sunk  by  the  large  quantity  of  debris  which  was  thrown 
upon  it. 

From  the  evidence  obtained  in  the  investigation  it  would  seem  that 
the  explosion  was  the  direct  result  of  a  choke-up  which  occurred  in  an 
elevator  leg.  Before  the  choke-up  was  noticed  and  the  motor  stopped,  so 
much  friction  had  developed  at  the  head  of  the  elevator  that  the  belt 
began  to  smolder  and  burn,  until  it  parted  and  dropped  down  through 
the  legs  into  the  elevator  boot  and  well.  The  dense  dust  cloud  raised  in 
the  legs  and  well  was  ignited  by  the  smoldering  or  burning  ends  of  the 
belt.  The  explosion  then  propagated  through  a  small  opening  in  the  well 
to  all  sections  of  the  plant.  On  account  of  the  peculiar  trough  plate  con- 
struction of  the  sides  of  the  bins  a  great  deal  of  dust  had  accumulated 
on  the  bin  walls.  This  dust,  thrown  into  suspension  by  the  force  of  the 
first  explosion,  was  ignited  by  the  flame  which  traveled  through  the  open- 
ing between  the  tops  of  the  bins  and  the  bin  floor.  Since  all  the  bins 
were  connected,  the  explosion  blew  away  the  entire  upper  portion  of  the 
plant. 


20 


Kansas    City,    Mo. 

In  a  very  disastrous  explosion  which  occurred  September  13,  1919, 
in  a  large  terminal  elevator  at  Kansas  City,  Mo.,  14  men  lost  their  lives 
and  10  were  seriously  injured  (Figs.  12  and  13).  The  elevator  was  par- 


FIG.   12. — View  showing  violence  of  explosion  and  damage  to  working  floor  and  shed. 
Explosion  originated  in  basement. 


FIG.    13. — Explosion  traveled    from   basement  through   man-lift   tower  to    "  texas  "    or   top 

of  elevator. 

21 


tially  wrecked,  the  property  loss  being  estimated  at  $650,000.  This  ex- 
plosion was  not  confined  to  any  one  portion  of  the  elevator,  but  propa- 
gated to  all  sections  of  the  workhouse. 

The  evidence  at  hand  indicates  that  the  explosion  originated  in  the 
basement,  in  the  vicinity  of  one  of  the  receiving  legs,  where  workmen 
were  cleaning  up  the  plant.  Great  difficulty  was  encountered  in  determin- 
ing the  exact  cause  of  the  explosion,  owing  to  the  fact  that  all  the  evidence 
required  to  establish  it  had  been  destroyed  on  account  of  the  force  of  the 
blast.  Judging  from  the  violence  of  the  explosion,  the  dust  in  this  plant 
must  have  been  very  inflammable. 

The  evidence  secured  from  one  of  the  workmen  indicated  that  the 
source  of  ignition  may  have  come  from  an  electrical  short  circuit.  This 
workman  stated  that  he  heard  a  sharp  cracking  noise  shortly  before  the 
explosion,  and  thought  that  he  had  seen  blue  flashes  of  flame  traveling 
along  the  electric  light  wires.  The  short  circuit  may  have  been  caused 
by  defective  extension  cords  or  the  breaking  of  an  unprotected  lamp 
bulb  in  the  dusty  atmosphere  present.  Workmen  in  the  basement  were 
known  to  have  been  using  extension  cords  at  the  time  of  the  explosion, 
and  it  is  possible  that  ignition  came  from  such  a  source. 

Spice    Dust    Explosion 

On  January  17,  1920,  4  firemen  were  killed  and  13  injured,  3  of  them 
very  seriously,  when  an  explosion  in  the  burning  mills  of  a  spice  company 
in  Cincinnati,  Ohio,  blew  out  the  east  wall  of  the  structure  (Fig.  14). 


FIG.    14. — At  extreme  right  can  be  seen  bridge  from  which  firemen  were  fighting  the  fire 
when  the  wall  was  blown  out  by  explosion  of  spice  di?St. 

22 


Since  the  early  newspaper  reports  stated  that  the  disaster  was  due 
to  an  explosion  of  tea  and  spice  dust,  an  investigation  was  conducted  to 
determine  if  possible  the  true  cause  of  the  explosion.  From  the  evidence 
that  was  secured  it  seems  that  the  walls  of  the  building  fell  without  any 
warning.  Tests  showed  the  spice  dust  to  be  very  inflammable,  and  it  is 
reasonable  to  conclude  that  the  explosion  or  force  which  blew  out  the 
walls  of  the  plant  was  probably  due  to  the  ignition  of  a  cloud  of  spice 
dust  which  was  formed  when  the  floors  in  the  building  fell. 

Aluminum  Dust  Explosion 

On  February  26,  1920,  a  disastrous  dust  explosion  occurred  in  an 
aluminum  goods  manufacturing  plant  at  Manitowoc,  Wis.,  as  a  result  of 
which  6  girls  lost  their  lives  and  5  were  seriously  injured  (Fig.  15). 


FIG.    15. — View    of    dust    collecting    system   showing    wire    as    found    in    fan    following   the 
explosion.     Buffing  brushes  used  can  be  seen  on  bench. 

The  explosion  originated  in  a  dust-collecting  system  used  in  collect- 
ing the  fine  particles  of  aluminum  dust  which  are  given  off  during  the 
process  of  putting  the  satin  finish  on  aluminum  goods.  This  process 
consisted  in  holding  the  aluminum  article  against  a  rapidly  revolving  steel 
brush. 

The  cause  of  the  explosion  is  attributed  to  a  piece  of  No.  7  iron  wire 
winding  itself  around  the  blades  of  a  blower  fan.  This  produced  a  spark 
which  ignited  the  fine  particles  of  aluminum  dust  in  suspension  in  the 
fan  and  gave  rise  to  the  explosion. 

23 


These  and  other  like  disasters  should  lead  the  chiefs  of  the  city  fire 
departments  to  make  an  earnest  effort  to  acquaint  themselves  and  their 
men  with  the  nature  of  dust  explosions  occurring  in  grain-handling  and 
inflammable  dust-producing  plants. 

Boissevain,  Manitoba,  Canada 

On  the  evening  of  December  6,  1919,  an  explosion  occurred  in  a 
flour  mill  at  Boissevain,  Manitoba,  Canada  (Fig.  16),  resulting  in  a  loss 
of  about  $15,000,  and 
injury  to  one  employee. 
The  explosion,  caused 
by  the  striking  of  a 
match  in  a  flour  bin, 
propagated  up  the  stair- 
way and  through  other 
openings  to  the  next 
floor  above  where  a 
secondary  explosion  did 
extensive  damage.  The 
brick  wall  at  one  side  of 
the  mill  was  blown  out 
and  the  warehouse  was 
damaged.  As  the  mill 
was  quite  clean,  very 
little  fire  occurred. 

Buffalo,  N.  Y. 

On  November  21, 
1919,  an  explosion  oc- 
cured  in  an  elevator  leg 
of  a  Buffalo  feed-grind- 
ing plant. 

At  the  time  of  the  ex- 
plosion workmen  were 
using  an  oxy-acetylene 
torch  to  cut  an  opening  in  the  boot  of  an  elevator  leg.  A  man  at  the 
top  of  the  leg  was  changing  a  spout  leading  from  the  elevator  head  to  a 
steel  conveyor.  After  as  much  of  the  steel  casing  had  been  cut  out  as 
was  necessary,  and  the  torch  had  been  extinguished  the  men  began  to 
hammer  the  plate  out  of  the  opening.  At  the  same  time  the  man  at  the 
top  of  the  elevator  leg  started  to  hammer  on  the  short  spout  leading  from 
the  head.  It  is  not  known  whether  the  torch  had  ignited  the  dust  in  the 
boot,  causing  it  to  smolder,  or  whether  the  hot  plate  ignited  the  dust, 
which  had  been  stirred  up  by  the  hammering.  The  explosion  that  fol- 
lowed traveled  up  the  back  leg  and  burst  it  open  for  a  distance  of  about 
30  feet,  in  spite  of  the  fact  that  a  portion  of  the  leg  was  open  and  a  vent 
provided.  No  fire  followed  the  explosion  but  several  employees  were 
injured  and  the  elevator  leg  was  damaged. 

24 


FIG.     16. — Explosion    blew    out    wall    of    upper    floor    after 
propagating   from   floor  below. 


Denver,    Colo. 

A  dust  explosion  followed  by  fire  caused  a  loss  of  over  $125,000  in 
a  large  Denver  flour  mill  on  January  20,  1920. 

At  first  the  cause  of  the  explosion  was  ascribed  to  the  production  of 
sparks  by  a  suction  fan  used  in  connection  with  the  dust-collecting  system. 
In  the  investigation  of  the  explosion  it  was  noted  that  the  fan  blades 
from  which  the  spark  was  said  to  have  originated  were  fastened  to  an 
overhanging  fan  shaft  by  means  of  a  feather  key  held  in  place  by  set 
screws,  with  a  one-inch  clearance  between  the  fan  blades  and  the  right- 
hand  side  of  the  outer  fan  casing,  but  none  on  the  left-hand  side  of  the 
casing.  The  theory  that  the  key  became  loose  in  the  fan  shaft  and  per- 
mitted the  revolving  fan  blades  to  strike  the  sides  of  the  fan  casing,  thus 
producing  sparks  which  in  turn  ignited  the  fine  flour  dust  coming  from 
the  roll  suction,  was  then  advanced.  Since  the  damage  resulting  from  the 
explosion  indicated  that  the  ignition  of  dust  took  place  in  the  dust-collect- 
ing system,  it  was  decided  that  ignition  could  be  attributed  to  the  pres- 
ence of  sparks  either  in  the  fan  or  from  the  rolls.  On  the  strength  of 
the  evidence  of  a  workman  on  the  roll  floor  that  one  of  the  doors  on  the 
roll  stands  had  been  blawn  open,  it  seems  reasonable  to  suppose  that 
the  explosion  originated  within  the  rolls  rather  than  in  the  fan. 


EXPERIMENTAL    WORK 

Theory    of    Dust    Explosions 

A  misunderstanding  seems  to  prevail  among  some  as  to  what  a  dust 
explosion  really  is.  These  assume  that  dusts  explode  in  the  same  man- 
ner as  high  explosives,  that,  for  instance,  a  sack  of  flour  or  a  package  of 
starch  in  the  kitchen  cabinet  might  suddenly  blow  up  as  gunpowder 
might.  This,  however,  is  not  the  case,  for  dusts  explode  in  the  same 
way  as  gas  does,  not  like  gunpowder  and  other  explosives.  Just  as  gas 
and  air  must  be  intimately  mixed,  and  in  the  proper  proportions,  in  the 
cylinder  of  an  internal  combustion  engine,  so  grain  dust  must  be  in  sus- 
pension in  the  air  as  a  cloud,  intimately  mixed  with  aif,  and  in  certain  pro- 
portions. Neither  the  mixture  of  gas  and  air  nor  that  of  dust  and  air  will 
explode  until  it  comes  in  contact  with  a  flame  or  some  other  source  of 
heat  of  sufficient  intensity  to  cause  it  to  ignite. 

Density  of  Dust  Cloud. — The  minimum  quantity  of  grain  dust  which 
must  be  in  suspension  before  an  explosion  can  be  initiated  has  not  yet 
been  determined.  It  is  reasonable  to  assume,  however,  that,  since  most 
of  the  grain  dusts  are  more  inflammable  than  coal  dust,  the  density  of  a 
cloud  of  grain  dust  need  not  be  greater  than  that  of  a  cloud  of  coal  dust 
through  which  an  explosion  will  just  propagate.  The  Bureau  of  Mines, 
of  the  United  States  Department  of  the  Interior,  has  found  this  density 
in  case  of  coal  dust  to  be  0.0253  ounce  of  dust  per  cubic  foot,  while  the 
French  Experiment  Station  has  shown  that  it  is  0.023  ounce  per  cubic 
foot. 

25 


Source  of  Ignition. — To  ignite  most  dusts  it  is  not  always  necessary 
to  bring  them  in  contact  with  a  large  source  of  heat,  such  as  an  open 
flame,  nor  a  very  high  temperature,  such  as  an  electric  arc.  Indeed,  a 
number  of  explosions  have  resulted  from  the  ignition  of  the  dust  by 
sparks  struck  as  foreign  materials  passed  through  the  machinery.  A 
spark  formed  by  the  discharge  of  static  electricity  will  ignite  many,  if  not 
all,  of  the  dusts  under  certain  conditions.  Some  of  the  dusts  are  ignited 
when  they  come  in  contact  with  bodies  having  a  temperature  of  540  de- 
grees C.  (1004°  F,).  which  is  well  below  dull  red  heat,  and  most  of  them 
will  ignite  when  brought  in  contact  with  a  body  having  a  temperature 
slightly  above  600  degrees  C.  (1112°  F.). 

Velocity  of  Propagation  of  Explosion. — The  velocity  of  propagation 
of  explosions  through  most  gas  mixtures  is  more  rapid  than  through  most 
dust  clouds,  although  in  a  few  cases  it  has  been  found  that  the  velocity 
of  flame  propagation  in  coal  dust  explosions  has  exceeded  the  maximum 
for  certain  gases.  In  only  two  tests  has  any  attempt  been  made  to  meas- 
ure the  velocity  of  propagation  of  the  flame  in  clouds  of  materials  other 
than  coal  dust.  One  indicated  that  the  velocity  through  a  cloud  of  wheat 
flour  dust  was  practically  the  same  as  that  through  coal  dust;  the  other 
that  the  propagation  through  a  cloud  of  powdered  starch  was  several 
times  as  rapid  as  through  the  coal  dust.  These  results,  however,  cannot 
be  considered  to  be  conclusive. 

Pressures  Developed  in  Explosions. — As  high  pressures  have  been 
developed  in  coal  dust  explosions  as  in  those  of  many  of  the  gases. 
Higher  pressures  have  resulted  from  the  explosion  of  several  of  the  grain 
dusts  than  from  the  explosion  of  coal  dust.  This  indicates  that  certain 
grain  dusts  are  more  inflammable  than  coal  dust,  and  quite  as  inflammable 
as  many  of  the  combustible  gases,  if  not  more  so. 

Conditions  for  Explosion. — Although  it  is  true  that  not  all  dusts 
will  explode,  the  dusts  from  any  material  which  burns,  or  is  readily  oxi- 
dized ,will  explode  under  certain  conditions.  The  ease  of  ignition  de- 
pends upon  various  factors,  such  as  the  composition  and  fineness  of  the 
material  and  the  amount  of  moisture  in  the  dust.  The  composition  of 
each  dust,  of  course,  is  fixed,  but  its  fineness  and  moisture  content  may 
vary.  Speaking  broadly,  the  finer  the  dust  and  the  lower  its  moisture 
content,  the  more  readily  ignition  takes  place,  or  the  greater  the  possi- 
bility of  an  explosion.  This,  however,  should  not  be  taken  to  mean  that 
a  coarse  or  a  moist  dust  will  not  ignite.  As  a  matter  of  fact,  if  the  dust 
is  fine  enough  and  dry  enough  to  form  a  cloud  or  to  be  thrown  into  sus- 
pension in  the  air,  it  can  be  ignited,  and  may  propagate  an  explosion. 

Propagation  of  the  Explosion. — When  a  plant  is  destroyed  by  an 
explosion  a  series  of  reports  resembling  a  roll  of  thunder  usually  is 
heard.  This  is  due  to  the  fact  that  several  explosions  follow  one  another 
so  rapidly  that  the  report  of  one  blends  in  with  that  of  the  next,  making 
a  continuous  roar.  For  example,  the  original,  or  primary,  explosion 


may  occur  in  a  grinding  machine  where  the  dust  cloud  is  confined  within 
a  small  space.  The  pressure  and  percussion  from  this  primary  explosion 
throws  into  suspension  the  dust  which  has  accumulated  on  beams,  ledges, 
and  floors.  This  dust  is  ignited  by  the  flame  of  the  primary  explosion, 
giving  rise  to  the  second  explosion,  which,  in  turn,  stirs  up  the  dust  in  the 
surrounding  portion  of  the  plant.  Thus  the  explosion  is  propagated 
throughout  the  plant,  or  as  far  as  dust  is  held  in  suspension  or  capable 
of  being  thrown  into  suspension. 

PREVENTION  OF  EXPLOSIONS.— To  prevent  explosions, 
therefore,  it  is  essential  not  only  that  all  possible  sources  of  ignition, 
such  as  open  flames,  the  presence  of  foreign  material  in  the  grinding 
machines,  an  accumulation  of  static  electricity,  improper  installation 
of  electrical  equipment,  and  an  inadequate  protection  for  all  electric 
lamps  in  a  dusty  atmosphere,  be  eliminated,  but  also  that  the  plant  be 
kept  scrupulously  clean,  thus  offering  no  medium  of  propagation  of 
the  primary  explosion  into  the  secondary,  and  more  extensive,  as  well 
as  more  disastrous,  explosion. 


Large   Scale   Tests 

Large  scale  tests  on  the  explosions  of  grain  dusts  were  conducted  at 
the  testing  station  of  the  Bureau  of  Mines  at  Bruceton,  Pa.,  where  a  large 
steel  gallery,  6  feet  in  diameter  and  220  feet  in  length,  with  vents  every 
few  feet  to  relieve  the  pressures,  is  used  in  testing  the  inflammability  of 
coal  dusts.  The  grain  dust  tests  were  made  under  the  same  conditions  as 
obtain  in  testing  coal  dust. 

One  pound  of  dust  to  each  linear  foot  of  the  gallery  was  spread  on 
four  shelves  on  both  sides  of  the  interior  of  the  gallery.  The  dust  was 
thrown  suddenly  into  suspension  and  ignited  at  the  closed  end  of  the 
gallery,  thus  propagating  the  explosion  well  out  through  the  open  end. 

Ordinary  wheat  flour,  corn  starch,  and  a  mixture  of  60  per  cent,  flour 
and  40  per  cent,  shale  dust  (ash)  were  used,  in  addition  to  the  coal  dust. 

Flour  and  coal  dust  behaved  alike,  the  explosions  produced  in  each 
case  being  propagated  at  about  the  same  velocity  and  developing  approxi- 
mately the  same  pressure.  The  flame  was  propagated  readily  through 
the  cloud  produced  from  a  mixture  of  flour  and  shale,  but  much  less 
readily  than  in  one  from  pure  flour,  and  with  but  slight  pressure. 

The  explosion  from  the  starch  dust  was  the  most  violent  of  all,  and 
developed  pressures  several  times  greater  than  those  from  the  coal  dust 
or  flour.  The  rate  of  propagation  also  exceeded  that  in  any  of  the  other 
tests.  Indeed,  the  percussion  was  so  great  that  windows  and  dishes  in 
buildings  two  or  three  miles  distant  were  shaken,  and  employees  of  the 
station  stated  that  it  was  the  most  violent  explosion  they  had  ever  seen  at 
the  gallery.  In  considering  the  relative  violence  of  the  explosions  from 
starch  and  from  flour,  it  should  be  borne  in  mind  that  the  flour  was 
coarser  than  the  starch  and  that  its  particles  had  a  tendency  to  adhere. 


Electrical    Equipment    and    Dust    Explosions 

Investigations  of  explosions  in  the  various  industries  where  inflam- 
mable dusts  'are  created  during  the  operating  processes  developed  the 
relation  of  the  electrical  equipment  and  appliances  to  the  cause  of  dust 
explosions.  In  some  instances  the  explosions  appeared  to  be  due  to  the 
ignition  of  the  dusts  by  electric  sparks  or  the  breaking  of  incandescent 
electric  lamp  bulbs  in  dust  clouds.  In  the  investigation  of  a  very  recent 
disastrous  explosion  resulting  in  large  loss  of  life  and  extensive  property 
damage,  one  of  the  probable  causes  suggested  was  the  ignition  of  the  dust 
in  suspension  by  an  electrical  source. 

The  lamp  manufacturing  companies  were  naturally  very  much  inter- 
ested in  this  phase  of  the  problem,  and  arrangements  were  made  for  co- 
operative experimental  work  relating  to  electric  lighting  equipment. 
Special  tests  are  already  in  progress  as  a  result  of  which  it  is  hoped  to 
determine  the  relation  of  electric  lamp  bulbs  to  explosion  and  fire  and 
develop  equipment  whi<ch  will  afford  extra  protection.  In  the  prelimi- 
nary tests  already  conducted,  explosions  were  readily  produced  when 
incandescent  lamp  bulbs  of  all  types  were  broken  in  dust  clouds. 


28 


Gaylord  Bros, 

Maker* 
Syracuse  N.  Y. 

PAT,  J AH.  2!  ,1908 


416813 


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